Nonionic surfactants are a preferred class of active agents for use in spermicidal formulations. For example, the nonionic surfactant nonoxynol-9 is a component in many commercially available spermicidal formulations. Spermicidal formulations are administered in the vaginal cavity for their local activity against human spermatozoa. It has been theorized that spermicidal agents exert their activity by inserting a hydrophobic moiety into the spermatozoan cell membrane. Upon insertion, the spermicidal agents disrupt the integrity of the cell membrane. This leads to an osmotic imbalance in the cell and, ultimately, cell lysis, thereby preventing sperm from fertilizing the egg and impeding conception.
Mixed experimental evidence exists as to whether non-ionic surfactants used in spermicides kill human immunodeficiency virus (HIV). In vitro experiments reveal that nonoxynol-9 inactivates HIV-1 completely. The inactivation may be through a mechanism similar to that proposed for the reduction of sperm motility. The hydrophobic portion of the nonoxynol-9 molecule may associate with hydrophobic fragments on the surface of the HIV virion leading to the derangement of the viral envelope and inactivation. The hydrophobic moieties of the virion include constituent lipids, sterols and proteins of the host cell membrane from which the viral envelope stems in addition to viral proteins.
Nonoxynol-9 suffers from a number of drawbacks. For example, in vivo clinical trials of products containing nonoxynol-9 do not show clear evidence of protection against HIV infection. Certain studies indicated that HIV infection rates were essentially equal when a population of women used vaginal contraceptives containing nonoxynol-9 or a placebo. Furthermore, vaginal irritation appears to increase with increased dose of nonoxynol-9.
A need exists for compounds which are more effective at lower doses, and which can achieve equal or greater contraceptive and anti-HIV efficacy with less irritation.